In a typical electrostatographic reproducing apparatus, a light image of an original to be copied is recorded in the form of an electrostatic latent image upon a photosensitive member. The latent image is subsequently rendered visible by the application of electroscopic thermoplastic resin particles, i.e., toner. The visible toner image is then in a loose powdered form that is easily disturbed or destroyed. The toner image is usually fixed or fused upon a support, which may be the photosensitive member itself or other support such as plain paper.
The use of thermal energy for fixing toner images onto a support member is well known. Fusing electroscopic toner material onto a support surface permanently by heat requires elevating the temperature of the toner material sufficiently to cause the constituents of the toner material to coalesce and become tacky. This heating causes the toner to flow to some extent into the fibers or pores of the support member. As the heated toner material cools and solidifies the toner material firmly bonds to the support.
Typically, toners comprising thermoplastic resin particles are fused to the substrate by heating to a temperature of between about 90° C. to about 160° C. Alternatively, depending upon the softening range of the particular resin used in the toner higher temperatures are used. Raising the temperature of the substrate substantially higher than about 200° C. is undesirable because of the tendency of certain substrates, for example, paper, to discolor at such elevated temperatures.
Several approaches to thermal fusing of electroscopic toner images are known. These methods include the application of heat and pressure substantially concurrently by various means: a rollerer pair maintained in pressure contact; a belt member in pressure contact with a rollerer; and the like. Heat may be applied by heating one or both of the rollerers, plate members or belt members. The fusing of the toner particles occurs when the proper combination of heat, pressure and contact time are provided. Balancing these parameters to fuse the toner particles is well known in the art, and can be adjusted for particular machines or process conditions.
During operation of a fusing system in which heat is applied to cause thermal fusing of the toner particles onto a support, both the toner image and the support pass through a nip formed between the rollerer pair, or plate or belt members. The concurrent transfer of heat and the application of pressure in the nip effect the fusing of the toner image onto the support. It is important in the fusing process that no offset of the toner particles from the support to the fuser member occurs. Toner particles offset onto the fuser member may subsequently transfer to other parts of the machine or onto the support in subsequent copying cycles, thus, increasing the background or interfering with the material being copied there. The so called “hot offset” occurs when the temperature of the toner is raised to a point where the toner particles liquefy and a splitting of the molten toner takes place during the fusing operation with a portion remaining on the fuser member. The hot offset temperature or degradation of the hot offset temperature is a measure of the release property of the fuser rollerer, and accordingly it is desired to provide a fusing surface, which has a low surface energy to provide the necessary release. To ensure and maintain good release properties of the fuser rollerer, it has become customary to apply release agents to the fuser members to ensure that the toner is completely released from the fuser rollerer during the fusing operation. Typically, these materials are applied as thin films of, for example, silicone oils to prevent toner offset.
Silicone oils are commonly used as release agents to aid transfer of the toner image to a substrate. Examples of silicone release agents are disclosed in U.S. Pat. No. 6,253,055B1 (silicone hydride oil); U.S. Pat. No. 5,991,590 (polydimethyl siloxane cationic liquid emulsion); and U.S. Pat. No. 5,531,813 (monoamino functional polyorganosiloxane). Silicone oils have several disadvantages related to thermal decomposition products caused by the high temperatures of the imaging process. The thermal decomposition of organosilicone oils results in the formation of toxic formaldehyde and silicates. The corona wire, which causes the electrostatic charge on an intermediate substrate, which holds the toner prior to transfusing onto a final substrate such as paper, becomes coated with deposits of silicates. Deposits of silicates on the corona wire reduces the efficiency of the corona wire, which results in reduced image quality. Additionally, silicone oils used as release agents are expensive.
Silicone oils also have the disadvantage that the amount of silicone oil needed as a release agent can transfer to the final substrate, such as paper, and prevent ink from adhering to the paper, which interferes with writing notes directly onto the paper. Also, the silicone oil may prevent Post-It™ Notes from adhering to the final substrate for the fused toner. Excess silicone oil causes a person's hands to feel oily after handling a substrate containing the silicone oil used as a toner release agent.
There exists a need for a non-silicone release agent to reduce the formation of formaldehyde and silicates. There exists a need for a less expensive substitute to the expensive silicone oil release agents.